PROJECT SUMMARY This project seeks to use real-time geospatial methods to investigate relationships between Global Positioning System (GPS)-defined activity space neighborhoods, social and sexual networks, and HIV prevention and care behaviors cross-sectionally and longitudinally among Black men who have sex with men (MSM) in the Jackson, Mississippi metropolitan statistical area (MSA) followed over a year. We will enroll 300 Black MSM in the CDC-funded MARI Study in the proposed study to address the aims of the research. Eligibility requirements include: self-report no restrictions to usual physical activity; no plans to move outside of Jackson MS MSA in the next year; and willingness to complete a two-week GPS protocol at four time-points over a year. Participants will wear the GPS device following protocols we have used in our previous feasibility research projects. In this longitudinal cohort study, three months after completing the initial 2-week GPS protocol, participants will carry the GPS device for an additional 2-weeks every three-months over the one-year study period?for a total of five times. GPS activity space environment data at baseline could potentially influence HIV outcomes over time and also having multiple GPS measures (at different time points) can better capture the breadth of people?s exposure to neighborhood-level factors and social/sexual networks. Findings from the proposed research will impact HIV prevention intervention activities. First, this research will inform specific neighborhood-level policy interventions. For example, increasing community efforts to combat lesbian, gay, bisexual and transgender hate crime neighborhood rates through increased local police attention in high-crime locations may be an HIV prevention intervention. Second, given that we will know the travel patterns of Black MSM, we will be able to identify optimal geographic locations for HIV testing/prevention interventions. This will advance the literature given that such interventions are seldom geographically targeted. Third, examining changes in spatial mobility (i.e. activity spaces) over time (four follow-up periods over a year) will be useful in knowing whether the risks of particular spaces change or remain constant because different neighborhoods will have different risk profiles. If these risk environments change, this suggests that prevention needs to be very dynamic and fluid and perhaps need rapid change-detection feedback loops. Finally, this research will also facilitate the identification of geographic locations suitable for recruiting Black MSM in research studies (an improved method of venue-based sampling), in this understudied group.